RGB Lasersystems q stick User manual

User Manual

User Manual
RGB Lasersysteme GmbH
Qstick Spectrometer
Version: 1.0.
Date: November 04, 201
This document is protected by copyright. Do not copy or publish this document or parts
of it without written permission of RGB Lasersysteme GmbH.
Product specifications and descriptions in this manual are subject to change without
notice. RGB Lasersysteme GmbH will not be responsible for errors and omissions in this
manual or for direct or incidental damages in connection with the use of this device or
information.
© 2012 RGB Lasersysteme GmbH
Donaupark 1
9 09 Kelheim
Germany
Telephone: [phone] --- 0
Website: http://www.rgb-laser.com
E-Mail: [email protected]

Contents
1 Introduction ...................................................................................................................... 1
1.1 Product Overview ....................................................................................................................... 1
1.2 System Requirements ............................................................................................................... 2
1. Package Contents....................................................................................................................... 2
2 Installation .........................................................................................................................
2.1 On-board USB memory drive .................................................................................................
2.2 PC Setup ........................................................................................................................................
2. Optical Setup ............................................................................................................................... 4
2.4 Troubleshooting ......................................................................................................................... 4
Operation ........................................................................................................................... 6
.1 Introduction ................................................................................................................................. 6
.2 Overview ....................................................................................................................................... 6
. Taking Spectra ............................................................................................................................. 7
.4 Spectrum Display ....................................................................................................................... 8
.5 Working with spectra ................................................................................................................ 9
.6 File Operations .......................................................................................................................... 10
.7 Spectrum Analysis .................................................................................................................... 11
.8 Absorption, Reflection and Transmission Measurements ........................................... 12
.9 Calibration .................................................................................................................................. 14
4 Software Development Kit ....................................................................................... 18
4.1 Prerequisites .............................................................................................................................. 18
4.2 Getting started .......................................................................................................................... 18
4. Classes Overview ...................................................................................................................... 18
4.4 Adding the SDK library to your project ............................................................................ 19
4.5 Taking a spectrum .................................................................................................................... 20
4.6 Deploying your project .......................................................................................................... 20
5 Technical Support ........................................................................................................ 21
5.1 Getting Help ............................................................................................................................... 21
5.2 Software Updates ..................................................................................................................... 21
6 Specifications ................................................................................................................. 22
7 Certifications and Compliance ................................................................................ 2

Introduction
1
1 Introduction
1.1 Product Overview
The Qstick contains a complete spectrometer in an extraordinarily small USB stick design.
The wavelength range covers the whole visible spectrum from 60 to 740 nm with a
resolution of 1.2 nm. It is controlled and operated by the spectroscopy software ‘‘Waves‘‘,
which not only includes unique sophisticated algorithms for data acquisition and
evaluation, but also provides these features through a clear and straightforward
interface. The Qstick includes an USB flash drive containing the device drivers and
application software.
Qstick Hardware Features
o Subminiature design
o Spectral resolution of 1.2 nm
o 2500 pixel CCD sensor
o Optical input via SMA fiber
o Controlled and powered via USB 2.0
Waves Software Features
o Take and display series of spectra
o Dynamic exposure control with dark spectrum interpolation
o Import most ASCII-based file formats
o Export as ASCII table to almost any numerical analysis software
o Comprehensive tools for displaying and analyzing spectra
o ‘‘Strip charts‘‘ for comparing characteristic values between multiple spectra
including peak follower
o Graph printing and export to PDF
o Dynamic peak finder (no need to set a threshold level)
o Automated wavelength calibration
o Dark spectrum interpolation
o Transmission, Reflection and Absorption measurements
o Colorimetry

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Applications
o Portable measurements
o Colorimetry
o Light analysis
o Forensic analysis
o System integration
o Process control and monitoring
1.2 System Requirements
o Windows 8, 7, Vista or XP ( 2 or 64 bit)
o .NET Framework Version .5 (available as a free download)
o USB 2.0
1. Package Contents
o Qstick spectrometer
o Waves spectroscopy software, device driver, and this manual as PDF (on the USB
memory drive included in the device)
o Printed user manual
Visit us at www.rgb-laser.com if you need any accessories for your spectrometer.

Installation
2 Installation
2.1 On-board USB memory drive
The Qstick includes an USB memory drive. When you connect the Qstick to a PC, this
drive appears with a new drive letter in the Windows Explorer. It contains the drivers,
application software and a PDF file of this manual.
2.2 PC Setup
Please install the software by double-clicking on the WavesSetup.exe file on this drive.
The setup package then installs the application software and the device driver.
Afterwards you can start taking spectra with the application software Waves.
The software is tested with 2 and 64 bit versions of Windows 8, 7, Vista and XP. It
requires at least the Microsoft .NET framework version .5, which is already installed on
most PCs. It also works with .NET framework version 4.0. If this framework is not installed,
you can download it from Microsoft’s website.
You can install the software on as many computers as you like. For example, you may
want to install it in the lab for measurements and in your office for further spectrum
analysis. Please visit our website for software updates.
The device driver for the Qstick spectrometer is not fully certified yet. If Windows displays
a warning, please choose to install the driver anyway. (You can be assured that is does
not contain any malicious software.)
The USB port needs to supply an electrical current of 200 mA, so you need to either
connect the spectrometer directly to your computer or to an externally powered USB
hub. A flashing red LED on the device indicated that the port does not supply enough
power.
When you start the Waves software, it automatically searches for the Qstick
spectrometers and, if it finds one, initializes the device. If you attached it just before, it
may take a few seconds before the spectrometer is properly recognized by the operating
system. The initialization takes a couple of seconds during which the software loads the
calibration data from the device.
If the software finds no or several spectrometers while starting, it displays a dialog
window from which you can choose a device or decide to use a ‘‘Simulated
spectrometer’’ instead. This simulated spectrometer can be used to evaluate the software
without connecting an actual device. You can access this dialog window later on by
choosing ‘‘Device Setup’’ from the File menu.

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2. Optical Setup
The light enters the Qstick spectrometer through a small slit. You can see this slit if you
look into the fiber optical connector on the front side of the device.
If the light you wish to measure is quite strong, you may simply point the spectrometer
towards it. For example, you can test the spectrometer by pointing it towards your
computer screen or your desk light.
In most cases, however, you’ll need a special optical probe to collect as much light as
possible. In order to guide the light from the probe to the spectrometer, use a fiber
optical cable with SMA connector like the one from the Qstick package.
We recommend standard fiber optical cables with a core diameter of 200 µm and a small
numerical aperture. If you’re using a fiber with a smaller diameter, you’ll get a slightly
better resolution and sensitivity, but you may find it more difficult to focus the light into
the fiber. If you’re using a larger fiber, the spectrometer cannot detect all of the light
coming out of the fiber and the stray light is slightly increased.
PLEASE NOTE: The calibration for the spectral sensitivity correction and the optical
power was made with a 200 µm fiber optical cable. If you use a different fiber or
especially if you just point the spectrometer towards the light source, the measured
spectrum might not be accurate. If you have a calibrated light source, you can always
recalibrate the spectral sensitivity for any optical setup (see chapter .9).
If you focus the light directly onto the entrance slit, you’ll get the best sensitivity and
lowest stray light if you make sure that:
o The focused light is centered on the entrance slit,
o the height of the light spot on the entrance slit is 200 µm or smaller and
o the numerical aperture of your focusing optics is close to 0.07, matching the
numerical aperture of the spectrometer.
If your focusing optics has a larger aperture than 0.07, you loose some intensity inside the
spectrometer. On the other hand, a numerical aperture significantly smaller may lead to a
decrease in resolution.
2.4 Troubleshooting
The green light on the spectrometer is off, the red light is flashing or lit
continuously and the device does not react
This indicates that the device has turned itself off because the USB port was not able to
supply enough power. This also may happen if the USB cable is too long or damaged.
Please disconnect the device and try a different USB port or cable.

Installation
5
Waves cannot find the device
Please disconnect and reconnect your spectrometer, close the ‘‘Device Config’’ window,
wait a few seconds and open this window again from the File menu. If this doesn’t help,
please restart your computer and try again.
Please also check our website www.rgb-laser.com for software updates.
If the software still cannot find the device, you may check the Device Manager in the
Windows Control Panel. Your spectrometer should show up as ‘‘Qstick’’ in the
‘‘Measurement and Control’’ branch. If your spectrometer is marked with an exclamation
or question mark, please remove the device, uninstall the software from the Windows
Control Panel, restart the computer and install the software again.
If your spectrometer is not listed at all in the Device Manager, please try a different USB
port. If the device does not work on one computer, but works on others, the USB port
may not provide enough power for the spectrometer. In this case, you’ll need to use an
externally powered USB hub.
If this doesn’t help either, please contact our Technical Support Team (see chapter 5.1).

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6
Operation
.1 Introduction
Waves was designed from the ground up to provide a clean and straightforward user
interface that does not stand in your way, without compromising advanced features or
precision.
If you are new to spectroscopy, you’ll find it easy to start using the software and taking
spectra without having to worry about details like calibration or dark spectra.
If you already have experience with other spectroscopy software, you’ll notice a few
differences:
o There is just one mode of operation that includes all relevant types of
measurements (absorption, irradiance, scope and so on) through a consistent and
clear interface.
o Waves favors a simple self-explanatory terminology instead of complicated terms
that need to be explained. For example, we use ‘‘Exposure time’’ instead of
‘‘Integration time’’, because the average user doesn’t really know what’s being
integrated here.
o There are no wizards to help you with complicated tasks, because wizards tend to
conceal the actual task. We believe it’s better to make these tasks accessible
through a clear and unified interface, so that you can understand what’s going on.
.2 Overview
When you start Waves, the software searches for an attached Qstick spectrometer. If it
finds one, it automatically initializes it. Afterwards, the software presents the main
window:

Operation
7
The main window consists of several panels:
1. The Exposure Toolbar, where you can start and stop taking spectra and set the
acquisition parameters.
2. The Spectrum List shows all spectra that are currently in memory.
. The Properties Panel consists of four tab pages and displays many parameters and
values of the spectrum currently selected in the Spectrum List.
4. The Main Diagram Panel shows all spectra marked with a check mark in the list.
5. The Display Parameters Panel determines how the spectra are displayed.
In order to get more screen space for the main diagram, the other panels can be
minimized by clicking on the buttons with two triangles next to the panel title.
. Taking Spectra
In order to take a spectrum, just choose an exposure time or select auto exposure and
click on one of the green buttons ([ ] for a single shot or [ ] to start a continuous
measurement). You can increase the exposure time in order to decrease the noise level. If
the amount of light detected during the exposure is too large for the CCD detector inside
the spectrometer, the spectrum appears saturated and a red ‘‘OVERLOAD’’ warning
appears at the top of the diagram. In this case, you need to decrease the exposure time.
You can further increase the sensitivity by averaging across multiple exposures with the
‘‘Temporal Averaging’’ setting.
If a spectrum acquisition takes longer than one second, you can monitor the progress in
the status bar at the bottom of the window. The acquisition may finish before the
progress indication reaches the end position, because the spectrometer is triggering on
the end of the exposure. You can stop the data acquisition by clicking on the red stop
button [ ].
If you choose auto exposure, the exposure time for each new spectrum is set
automatically based on the intensity of the previous spectrum. It may take a few spectra
before the auto exposure control has reached its optimum. In auto exposure mode, you

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8
can set a maximum exposure time in order to prevent very long exposure times in cases
when there is simply no signal.
Spectra can be taken with or without spectral sensitivity correction (see chapter .9 for
more details). If the lightmeter button [ ] is selected, the spectral sensitivity of the
spectrometer is automatically corrected and the intensity axis is measured in nW/nm.
PLEASE NOTE: If you take a spectrum with spectral sensitivity correction, the noise in the
spectrum is not evenly distributed, because some parts of the spectrum are more
amplified than others. On the other hand, if this button is not selected, the spectral
sensitivity is not corrected and the intensity axis displays values as they are produced by
the spectrometer hardware. In this case, you may find an uneven distribution of the
sensitivity across the spectrum. For precise measurements, it is recommended to turn on
spectral sensitivity correction.
Dark spectra for the spectrometer are stored in the device and used automatically when
taking spectra (see chapter .9 for details). If you have background radiation, you can
compensate for it by taking a background spectrum (see chapter .8). In the Exposure
Toolbar you can also select the triggering mode and choose a reference spectrum for
absorption, reflection and transmission spectroscopy (see chapter .8).
.4 Spectrum Display
The Main Diagram Panel displays all spectra that are marked by a check mark in the
Spectrum List. If no spectrum is checked in the list, then the currently selected spectrum
(marked by a gray bar) is displayed. You can check and uncheck all spectra at once by
clicking on the corresponding button [ ] or [ ] on top of the Spectrum List.
The peaks in the spectra are automatically determined. This not only works pretty reliable
for clearly defined peaks, but also for those lying in the side of another peak or those that
are just above the noise level. If necessary, you can fine-tune the parameters for finding
the peaks by choosing ‘‘Peak Finder Parameters’’ from the Tools menu. In this window
you can choose three settings:
o ‘‘Absolute threshold’’ determines how much a peak must be above the noise level
in order to be considered as a peak.
o ‘‘Relative threshold’’ describes how large a peak must be compared to the local
minima before and after it in order to be considered as a peak.
o ‘‘Position threshold’’ determines how much of the top part of the peak is
considered when calculating the peak position.
Peak positions and widths are only displayed for the currently selected spectrum. The
peak positions, heights and widths are also displayed in the Properties Panel and can be
exported by choosing ‘‘Export Peaks’’ from the File menu.
In the Display Parameters Panel below the diagram you can select how the spectra are
displayed. These settings affect the diagram display, but do not modify the actual data.
Here you can change the scaling of both axes, the unit of the wavelength axis, turn the

Operation
9
display of the grid, peak positions and peak heights on and off and see the coordinates of
the current position of the mouse pointer.
If you zoom into the wavelength axis, a scrollbar appears at the bottom of the diagram
for easily moving the displayed part of the spectrum. Alternatively, you can grab and
move the axis with the mouse. You can also drag the intensity axis in order to change the
maximum value and quickly enlarge weaker parts of the spectrum.
If you would like to determine the intensity value at the position of the mouse pointer
relative to a reference value, just move the mouse to that reference value, click with the
right mouse button and choose ‘‘Set reference level’’.
You can select a single wavelength or a range of wavelengths by clicking or clicking and
dragging in the diagram. This selection can be used to compare wavelength values, to
display statistical data just for the selection (see chapter .5) and to zoom into it (by right-
clicking).
.5 Working with spectra
In Waves, you can have several spectra loaded at the same time for easy comparison and
analysis. On the upper left side you can see the Spectrum List. Whenever you take a new
spectrum, it appears in this list as ‘‘current spectrum’’ and overwrites any previous
‘‘current spectrum’’. If you would like to keep this spectrum and take another one, just
click on the single push pin button [ ]. This prevents the current spectrum from being
overwritten. A new spectrum you take is then appended to the list. Giving the ‘‘current
spectrum’’ a new name also prevents it from being overwritten. You can also choose to
keep all new spectra by selecting the button with multiple push pins [ ] in the Exposure
Toolbar.
When you have multiple spectra in the list, one spectrum is always selected (marked by a
gray bar). All metadata and additional information for this spectrum is displayed in the
Properties Panel on the lower left side. The Properties Panel has five Tab pages:
o eneral: Displays spectrum metadata. ‘‘Name’’ corresponds to the name in the
Spectrum List. ‘‘User’’ is automatically set to the current Windows user name, but
can be changed. ‘‘Sample’’, ‘‘Light’’ and ‘‘Comments’’ can be freely edited by the
user. You can change the color of the spectrum by clicking on the color box. Please
note that ‘‘User’’, ‘‘Sample’’, ‘‘Light’’ and ‘‘Comments’’ is the same for all spectra in
the list.
o Values: Displays statistical values both for the whole spectrum and within the
selection (if you have selected a range of wavelengths in the diagram).
o Color: Displays colorimetric values. For precise color measurements please also
read the section on calibration accuracy in chapter .9.
o Peaks: Displays peak positions, heights and widths. This list can be save to a file by
choosing ‘‘Export Peaks’’ from the file menu.
o Data: Displays a list of all values of the spectrum.

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Some of the values in the Properties Panel are saved when saving the spectrum to a file.
The others are recalculated when the spectrum is reloaded.
.6 File Operations
You can save the selected spectrum or the whole Spectrum List using the commands in
the File menu. You can also open spectrum files to load them back into Waves for further
evaluation (sounds obvious, but surprisingly, many spectroscopy applications don’t even
support this).
The file format for spectra is a simple ASCII table with columns delimited by the TAB
character and some header lines containing the metadata. This allows the spectrum files
saved by Waves to be read by almost any numerical analysis software like Origin, Excel or
Matlab. The default file extension for these files is ‘‘.spz’’. If you click on an .spz file in
Window Explorer, it is opened with the Waves application.
In Waves, you can also open spectrum data files written by other applications, if they are
saved as ASCII tables or .csv files. Waves tries its best to automatically determine the file
structure and is able to open many different file formats.
1
You can print spectra by choosing ‘‘Print’’ from the file menu. If you choose the page
orientation as ‘‘Landscape’’, the spectrum diagram is printed across the whole page. If
you choose ‘‘Portrait’’, the diagram is printed on the upper half of the page and the lower
half shows selected metadata and values.
The printing options are designed for the most common tasks. If you have further specific
requirements for printing, you may also decide to export the diagram and then use a
graphical design software or word processor for printing.
You can export the diagram either as a bitmap image or as a PDF vector graphic. Both
options are available by choosing ‘‘Export’’ from the File menu.
After choosing a file name, you can set the height and width of the image and the
resolution, if applicable. Please note that the text sizes and line widths are constant.
Therefore, if you choose a larger export size, the labels and line widths appear to be
smaller.
1
In case you have a spectrum file written as ASCII data and you are unable to open it in Waves, please
contact our Technical Support Team and we’ll see if we can include an import filter for this file format.

Operation
11
.7 Spectrum Analysis
The Analysis menu offers several ways to evaluate and modify spectra:
Adjust Offset
This adds a constant value to all data points of the selected spectrum. The software
suggests a estimated value for compensating an offset, but you may also choose any
other value.
Normalize
This multiplies all data points of the selected spectrum by a constant factor. The default
factor is chosen for the maximum value to be scaled to 100.
Differentiate
This differentiates the spectrum with respect to the wavelength.
Spectral Averaging
This substitutes each data point by the average of the surrounding data points. You can
choose how many data points to include in the averaging. This is also known as ‘‘Boxcar
Averaging’’.
Arithmetic Operations
This creates a new spectrum by adding, subtracting, multiplying or dividing two spectra.
Adjust Wavelength
This allows to assigns a new wavelength scale to all spectra in the list based on the
parameters for the fourth-order polynomial function used for wavelength calibration. It
may be useful if you took spectra with an incorrect wavelength calibration.
Duplicate
This creates a copy of the selected spectrum and may be useful if you would like to
modify a spectrum, but also keep the original one.
Peak Width Diagram
This opens a window displaying the widths of the detected peaks (Full width at half
maximum).

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Show Strip Chart
You can use the Strip Chart window to display a characteristic spectrum value as a
function of another value for all spectra in the list. The most common task is to display
the temporal evolution of a characteristic value. This window can be kept open while
taking new spectra to see the changes as they happen.
In the lower left side of the Strip Chart window, you can choose which values to assign to
the x and y axis of the chart. You can choose all numerical values that are displayed in the
Properties Panel in the main window. If you want to view the temporal evolution of a
value, choose this value for the y axis and either ‘‘Number in List’’ or ‘‘Time’’ for the x axis.
If you choose ‘‘Value from name’’ as x or y axis, the software tries parse the name of each
spectrum into a number. So for example, if you have a list of spectra that are named ‘‘T =
10. °C’’, ‘‘T = 15.2 °C’’ and so on and you choose ‘‘Value from name’’, these temperature
value are used for the corresponding axis.
In the Strip Chart diagram, the currently selected spectrum is marked by a slightly larger
point. Points corresponding to spectra that are currently not visible in the main window
are drawn in a lighter red color.
Show Loupe
This opens a window with a magnified display of the spectrum around the mouse
pointer. It may be used in order to study small features in the spectrum as an alternative
to zooming in.
.8 Absorption, Reflection and Transmission Measurements
Principle
In absorption, reflection and transmission spectroscopy you direct light from a
broadband light source onto a sample. Then you take a spectrum (λ) of the light that is
transmitted through or reflected from the sample. In order to get meaningful results that
are independent of the light source, you also take a spectrum of the light source 

(λ) as
a reference.
The spectral transmittance (λ) or reflectance is then simply the fraction of transmitted
or reflected light:
(λ) =  (λ)


(λ)
This formula gives values in the range between 0 and 1. The transmittance is usually
written as a percentage. The spectral absorbance (λ)is defined as:
(λ)= log 

(λ)
(λ)

Operation
1
Please note that the absorbance is sometimes defined as the base 10 logarithm and
sometimes as the natural (base e) logarithm. In Waves, you can choose in the Options
window from the File menu which logarithm to use.
Measurement
In order to measure absorption, reflection or transmission you need to take a reference
spectrum of the light source first. If your measurement setup is not in complete darkness,
it is also generally recommended to take a background spectrum before the
measurement.
To take a background spectrum, turn off the light source, set an appropriate exposure
time and click the ‘‘Take Background Spectrum’’ button [ ] on the Exposure Toolbar. In
order to minimize noise, you may also want to use temporal averaging. When you’ve
taken a background spectrum, you can select the ‘‘Use Background Spectrum’’ button [
]. If you take a spectrum afterwards, the background spectrum is automatically
subtracted from the measured spectrum, eliminating unwanted background signals.
To take a reference spectrum for transmission or absorption spectroscopy, turn on the
light source again, remove the sample, set an appropriate exposure time and temporal
averaging and click the ‘‘Take Reference Spectrum’’ button [ ]. After selecting the ‘‘Use
Reference Spectrum’’ button [ ], you can take spectra of your sample for measuring
absorption or transmission.
To take a reference spectrum for reflection spectroscopy, you need a white reference
sample to calibrate the setup for 100 % reflection. However, all real-world reference
samples have a reflection of less than 100 % and an uneven spectral distribution.
Therefore, for accurate measurements you also need to supply a reference spectrum for
your reference sample. To take a reference spectrum, place the white reference sample
where you’ll later place the sample to be measured. Then set an appropriate exposure
time and temporal averaging and click the ‘‘Take Reference Spectrum’’ button [ ]. In the
following dialog window, you can also specify a data file that includes a calibrated
spectrum of your reference sample. After selecting the ‘‘Use Reference Spectrum’’ button
[ ], you can measure reflectivity spectra.
The y axis of the spectrum now shows the relative intensity of the measured spectrum
compared to the reference spectrum. In the ‘‘Options’’ dialog from the File menu you can
choose different units for displaying the spectra:
o Ratio shows the ratio of the measured spectrum to the reference spectrum as in
the formula for (λ) above.
o Percentage shows the same value (λ), but written as a percentage (i.e. multiplied
by 100).
2
This unit is usually used for transmittance.
o Absorbance shows the spectral absorbance (λ) according to the formula above.
You can choose between natural and base 10 logarithm.
2
Please note that „percent‘‘ means nothing else than ‘‘divided by 100’’.

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These options only determine how to display the spectra in the diagram. The do not
modify the actual spectrum data.
If your light source does not cover the full range of the spectrometer, the calculated
spectrum may show large amounts of noise outside of the wavelength range of your
light source. This is normal and reflects the fact that the measurement has a large
uncertainty at these wavelengths.
These measurements are quite sensitive to changes of the sample illumination. If in
doubt, you may want to take another reference spectrum to check if it is still valid.
.9 Calibration
The calibration for the wavelengths, dark spectra and spectral sensitivity are stored on
the device and loaded automatically during device initialization. So in contrast to almost
any other spectroscopy software, you don’t need to worry about taking dark spectra and
other calibration parameters, it’s all done automatically.
If the device has been used for a long time or if you need a very precise measurement,
you can easily recalibrate the spectrometer within Waves, if you have a suitable light
source. Recalibration may also be required if the device temperature is outside of the
calibrated temperature range. The device temperature is continuously monitored by the
spectrometer and a warning is displayed, if the temperature has changed considerably.
After you have recalibrated the spectrometer, you can always restore the factory
calibration in the ‘‘Device Properties’’ window from the File menu.
Calibration Accuracy
The wavelength calibration is very accurate and changes only little with time or
temperature. Therefore, most users won’t ever need to recalibrate the wavelengths.
The dark spectrum calibration depends on the temperature. If the temperature has
changed considerably, a warning message is displayed recommending recalibration.
However, if in doubt or if you need as little noise as possible, you can always easily
recalibrate it because no calibration light source is required.
The calibration for the spectral sensitivity depends a lot on your optical fiber, your
measurement probe and how the light is coupled into the spectrometer. During
production of the Qstick spectrometer, we don’t know what your optical setup is going
to be. Therefore the factory calibration for the spectral sensitivity and especially the
absolute intensity is not to be considered as a precise measurement, but rather as a first
estimate. If you require precise intensity measurements, you’ll have to recalibrate the
sensitivity of the whole system including fiber and probe.
In addition, please note that after changing the exposure time, it takes a few spectra
before the CCD sensor inside the spectrometer reaches its new equilibrium. This means
that after changing the exposure time, the intensities of the following 5 to 10 spectra

Operation
15
may not be as accurate as later measurements. Therefore, for precise measurements we
recommend not to use the auto-exposure feature and to set a fixed exposure time
instead.
Wavelengths
The mapping of the individual pixels of the spectrum to wavelengths is done using a
third-order polynomial. The four parameters for this function are measured during
manufacturing and stored in the device. Usually, this wavelength calibration does not
change. Therefore, in most cases you don’t need to recalibrate the wavelengths.
However, if the ambient temperature has changed substantially, if the device has been
used for a very long time or if you just would like to make sure that the wavelengths are
really correct, you can recalibrate the wavelength if you have a suitable light source with
several sharp atomic emission lines. These wavelength calibration sources are usually
low-pressure gas discharge lamps filled with Krypton, Neon, Mercury, Argon or Xenon
gas.
To recalibrate, take a spectrum of this light source first. Make sure that the relevant peaks
are automatically detected. If not, adjust the ‘‘Peak Finder Parameters’’ in the Tools Menu.
Then choose ‘‘Calibrate Wavelengths’’ from the Tools menu. In the ‘‘Reference Spectrum’’
combo box select the type of light source used. If you don’t find your light source in the
list, you need to supply your own calibration lines. In this case, please take a look at the
‘‘CalibrationLines xxx.dat’’ files in the installation folder on your hard drive and
create a new similar file containing the spectrum lines of your light source.
After you have selected your light source, click on ‘‘Start Fit’’. The software tries to match
the peaks in the measured spectrum and the given spectrum lines for your light source
automatically. Not all of the given spectrum lines have to be present in the measured
spectrum, but all measured peaks must be known spectrum lines. If a match has been
found, the average deviation is displayed. If the match seems to be successful, it is
displayed in green, otherwise in red. You can also graphically display the deviations by
clicking on ‘‘Show Deviations’’. If the measured peaks have successfully been identified,
you can set the four new wavelength calibration parameters by clicking on the ‘‘Save’’
button and confirm by clicking ‘‘OK’’. The new wavelength calibration is then saved to the
device.
Dark Spectra
Inside the Qstick spectrometer, the spectra are detected with a CCD line sensor. Like all
image sensors, this sensor detects a small signal even if there is no light entering the
spectrometer. This signal depends on the individual pixel, the exposure time and the
temperature. In order to obtain a precise measurement with a small noise level, this ‘‘Dark
Spectrum’’ must be taken while no light enters the spectrometer and then subtracted
from the actual measurement.

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For your Qstick spectrometer, this dark spectrum has already been taken, is stored in the
device and automatically subtracted from the measured spectrum each time you take a
new spectrum. Because the dark spectrum depends on the exposure time in a non-linear
way, there are actually multiple dark spectra stored in the device for a certain number of
exposure times. The dark spectrum that is needed for a chosen exposure time is then
obtained by interpolating between these dark spectra.
In case you find that the spectra you get are not zero on the average, even if no light
enters the spectrometer, then you probably need to recalibrate the dark spectra. You can
also check the dark spectrum calibration using the ‘‘Calibrate Dark Spectrum’’ window
(see below).
To recalibrate the dark spectra, simply close the spectrometer entrance, make sure that
no light enters the device and choose ‘‘Calibrate Dark Spectrum’’ from the Tools menu.
Then click the ‘‘Take’’ button and go for a coffee. After a few minutes the software has
taken dark spectra for a series of exposure times. You can check the new dark spectra by
clicking on the ‘‘Test Button’’. While the test is running, you can in the lower diagram the
spectra taken without (red) and with (green) dark spectrum correction. In the upper
diagram you can see the noise level, also without (red) and with (green) dark spectrum
correction for a series of exposure times. You can see that the noise level of the raw data
(red) increases significantly with increasing exposure time. With dark spectrum correction
(green) however, the noise level should remain pretty much at the same level for
exposure times less than 1 second and increase slower for exposure times larger than 1
second. If you find this to be the case, close the window by clicking on the ‘‘OK’’ button
and the new dark spectrum calibration is saved into the device. Otherwise you may
calibrate again or click ‘‘Cancel’’.
Spectral Sensitivity
Like in all spectrometers, the sensitivity of the Qstick spectrometer is not uniform across
the spectrum, but depends on the wavelength. This is called ‘‘Spectral Sensitivity’’ and
can be corrected by dividing each value of the spectrum by the corresponding sensitivity.
This sensitivity calibration is also stored in the device. However, it is not always used
when taking spectra, because if the sensitivity is corrected, the noise level is unevenly
distributed across the spectrum. Instead, you can choose to use the spectral sensitivity
correction by selecting the ‘‘lightmeter’’ button in the Exposure Toolbar.
If you would like to recalibrate the spectral sensitivity, you need a light source with a
continuous spectrum (like a tungsten halogen lamp) and a calibrated spectrum for this
lamp.
To recalibrate, take a spectrum of your light source with spectral sensitivity correction
turned off. Make sure the spectrum contains as little noise as possible by using a strong
light source, a suitable exposure time and use Temporal Averaging. Then choose
‘‘Calibrate Spectral Sensitivity’’ from the Tools menu. Click on the ‘‘Load reference data’’
button to load the calibrated reference spectrum (in other words: a spectrum file that
shows how your light source really looks like). Based on the measured spectrum and this